Method and apparatus for pattern inspection

ABSTRACT

Because a mirror electron imaging type inspection apparatus for obtaining an inspection object image with mirror electrons has been difficult to optimize inspection conditions, since the image forming principles of the apparatus are different from those of conventional SEM type inspection apparatuses. In order to solve the above conventional problem, the present invention has made it possible for the user to examine such conditions as inspection speed, inspection sensitivity, etc. intuitively by displaying the relationship among the values of inspection speed S, inspection object digital signal image pixel size D, inspection object image size L, and image signal acquisition cycle P with use of a time delay integration method as a graph on an operation screen. The user can thus determine a set of values of a pixel size, an inspection image width, and a TDI sensor operation cycle easily with reference to the displayed graph.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 11/698,025 filed Jan. 26, 2007. Priority is claimed based on U.S.application Ser. No. 11/698,025 filed Jan. 26, 2007, which claims thepriority of Japanese Patent Application No. 2006-027861 filed on Feb. 6,2006, the content of which is hereby incorporated by reference into thisapplication.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus forinspecting an electrical defect of a microstructure circuit formed on asemiconductor wafer.

BACKGROUND OF THE INVENTION

As a method for detecting a defect of a circuit pattern formed on awafer by comparing images in a manufacturing process of a semiconductordevice, for example, a pattern comparing inspection method is disclosedin JP-A No. 258703/1993. The method uses an SEM in which, a pointfocused electron beam is scanned. The SEM type inspection apparatus ishigher in resolution than optical inspection systems and it has afeature for enabling such an electrical defect as a connecting failureto be detected. However, because the SEM type inspection apparatus scansan electron beam on a specimen surface two-dimensionally to obtain animage, the scanning time is long. This disadvantage will become asubstantial obstacle for reducing the inspection time.

As an electron beam inspection method that has successfully reduced theinspection time, for example, the JP-A No. 249393/1995 discloses aprojection type inspection apparatus, which illuminates a rectangularelectron beam onto semiconductor wafer and forms an image of buckscattering and secondary electrons with use of electron lenses. Theprojection type inspection apparatus can illuminate an electron beamwith a larger current than that of the SEM type at a time, therebyobtaining a plurality of images collectively. The projection type isthus expected to form images more quickly than those of the SEM type,that is, the scanning electron type.

On the other hand, a secondary electron mapping type inspectionapparatus cannot obtain a sufficient resolution due to the aberration ofthe objective lens, thereby it is difficult to obtain a required defectdetection sensitivity. The JP-A No. 108864/1999 points out suchdisadvantages of the apparatus. The JP-A No.108864/1999 discloses amirror electron imaging type wafer inspection apparatus that useselectrons pulled back (hereunder, to be referred to as mirror electronsor mirror reflecting electrons) before colliding with a specimen due toa negative electric field formed just above the wafer as imagingelectrons.

Here, the mirror electron imaging type wafer inspection apparatus willbe described. The mirror electron imaging type wafer inspectionapparatus obtains an image to be used for inspection with use of amirror electron microscope. An inspection image is obtained byilluminating an electron beam onto a specimen and forms an image of thereflecting electron beam. At this time, a negative potential is appliedonto the surface of the specimen in advance so that the illuminatedelectron beam is reflected on a specific equipotential surface in thevicinity of the specimen surface without reaching the specimen surface.The electrons reflected on an equipotential surface in the vicinity ofthe specimen surface such way are referred to as “mirror electrons”.Because the equipotential surface of the specimen surface is influencedby the information of an unevenness and a potential change of thespecimen surface itself, the image to be obtained is also influenced bythe information of the unevenness and the potential change of thespecimen surface when the mirror electrons are imaged. Consequently,shape and electrical defects of the specimen surface can be detected bycomparing such a mirror electron image with a reference image,respectively.

SUMMARY OF THE INVENTION

As described above, the mirror electron imaging type wafer inspectionapparatus differs completely from any of the conventional SEM typeinspection apparatuses. Consequently, to put the mirror electron imagingtype wafer inspection apparatus for practical use, it is needed to thinkout a method for setting inspection conditions optimized for theapparatus. Under such circumstances, it is an object of the presentinvention to realize an inspection condition setting method optimizedfor the object mirror electron imaging type wafer inspection apparatusand make it easier to operate the apparatus.

Upon thinking out a method for setting such inspection conditionsoptimized for the mirror electron imaging type wafer inspectionapparatus, the present inventor has examined the followingcircumstances.

A mirror electron imaging type wafer inspection apparatus employed in asemiconductor device manufacturing line is often used for defectinspection in all or some specific portions of every wafer flowing onthe manufacturing line. Thus where an inspection process is to beinserted between semiconductor processes and how long time is to bespared for the inspection process should be determined carefully bygiving consideration to the productivity of the semiconductormanufacturing line. In other words, if the inspection process isdesigned in detail to improve the yield, the productivity is lowered inproportion to an increase of the inspection time. Furthermore, when theinspection time is reduced, both the inspection accuracy and theproductivity are lowered. Such way, in each of various manufacturinglines for improving the productivity, in which the defect generatingrate, defect generating process, and productivity are different fromeach another, there is an optimized inspection time that should beemployed for the object line specifically. Thus the inspection timecomes to be varied among those manufacturing lines. This is why theinspection speed should be set flexibly for the mirror electron imagingtype wafer inspection apparatus so as to make inspections mostefficiently by giving consideration to the circumstances specific toeach of such various semiconductor device manufacturing lines.

The inspection speed of the mirror electron imaging type waferinspection apparatus means an area of a wafer that can be inspected perunit time. FIG. 2 shows the arrangement of pixels for composing aninspection object image. In FIG. 2, each cell means a pixel 201. Thecall is usually a square of which the length of this side is representedby D. An inspection image of the mirror electron imaging type waferinspection apparatus is obtained with use of a time delay integrationdata acquisition method (TDI method). In the TDI method, integration ismade by sending image signals in the vertical direction of the imagesynchronously with the movement of the wafer (as shown with a whitearrow in FIG. 2). The cycle in which one signals of pixel are sent inthe vertical direction is defined as P. And the length in a direction(horizontal direction in FIG. 2) normal to the movement of the wafer inthe image region is defined as L. The image data of length L×width Darea (gray region shown in FIG. 2) is sent in a cycle P to an imageprocessing apparatus. Consequently, the inspection speed S can bedescribed by using D, P, and L in the following expression:

S=D×L×P.

To operate the apparatus at an optimized speed, therefore, the user isrequested to satisfy the relationship among D, L, and P shown above andadjust the D, L, and P values so as not to degrade the inspectionsensitivity. Particularly, in the case of the mirror electron imagingtype wafer inspection apparatus, the pixel size optimized for inspectionis changed depending on the magnification of the imaging optical systemfor mirror reflecting electrons. This change depends on thecharacteristics such as the material, structure, etc. of the specimen.And such characteristics are never generated in any of SEM and secondaryelectron projection type electron optical systems; the characteristicsare specific to the mirror optical systems. The user of the apparatus,therefore, is requested to adjust the D, L, and P values by givingconsideration to the magnification of the optical system.

Conventionally, the apparatus manager and the apparatus developer haveset such D, P, and L values with the method of trial and error by givingconsideration to the characteristics of the mirror electron imaging typewafer inspection apparatus and the inspection object, which has leadsvery troublesome condition setting. Furthermore, usually the user'sinterest is just the inspection speed. The user would thus feel verytroublesome when requested to set such conditions and will come to havea feeling of confusion when operating the apparatus.

In order to solve the above described conventional problems, therefore,the present invention has enabled such S, D, L, and P values to bedisplayed on an operation screen so that the user can examine suchconditions as inspection speed, inspection sensitivity, etc.intuitively. Furthermore, the present invention has provided a processnewly for converting user determined conditions to conditions foroperating an electron optical system, a time delay integration typeimaging device, and a wafer moving stage respectively so that the usercan make inspections in accordance with the circumstances of varioussemiconductor manufacturing lines without understanding the details ofthe inspection apparatus.

According to the present invention, therefore, it is possible to setsuch conditions as optimized pixel size, illuminating area size, etc. toeasily realize an inspection speed capable of preventing ansemiconductor device manufacturing line from delay so that the user caninspect defects of each semiconductor pattern efficiently underoptimized conditions. Because such inspection conditions can be seteasily such way, the total inspection time from condition setting to endof inspection can be reduced. And because the apparatus can be operatedeasily, the apparatus will also have advantages in sales policy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing a basic configuration of a mirrorelectron imaging type wafer inspection apparatus;

FIG. 2 is a diagram for describing how to obtain an inspection imagewith a TDI image acquisition method;

FIG. 3 is a diagram for describing an example of an inspection conditionsetting screen;

FIG. 4 is a diagram for describing another example of an inspectioncondition setting screen;

FIG. 5 is a diagram for describing still another example of aninspection condition setting screen;

FIG. 6 is a diagram for describing principles of defect detection with amirror electron image;

FIG. 7 is a diagram for describing an example of a defect expansioneffect in an inspection object image with a mirror electron imagingmethod;

FIG. 8 is a diagram for describing an application example of the presentinvention to a mirror electron imaging type wafer inspection apparatus;

FIG. 9 is a diagram for describing an example of an inspection conditionsetting screen; and

FIG. 10 is a diagram for describing an application example of thepresent invention to a mirror electron imaging type wafer inspectionapparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, a description will be made in detail for a configuration of amirror electron imaging type wafer inspection apparatus in a preferredembodiment of the present invention with reference to the accompanyingdrawings.

First Embodiment

FIG. 1 shows an example of a hardware configuration of the mirrorelectron imaging type wafer inspection apparatus in the preferredembodiment of the present invention. In FIG. 1, vacuum pumps, theircontroller, pipes for evacuating systems, etc. are omitted.

At first, main elements of the electron optical system of the apparatuswill be described. An illuminating electron beam 100 a emitted from anelectron gun 101 is focused by a condenser lens 102 and deflected by anExB deflector 103 to form a cross-over 100 b, then illuminated onto aspecimen wafer 104 as an approximate parallel flux. In FIG. 1, althoughonly one condenser lens 102 is used, a plurality of lenses may becombined into a lens system to optimize the optical conditions. Theelectron gun 101 is usually a Zr/0/W type Schottky electron source. Suchvoltages and currents as an extracting voltage applied to the electrongun 101, an accelerating voltage to extracted electrons, a heatingcurrent of an electron source filament, etc. required for operating theapparatus are supplied and controlled by an electron gun controller 105.

The ExB deflector 103 is disposed in the vicinity of an imaging plane100 d of an imaging electron beam 100 c. At this time, an aberrationoccurs in the illuminating electron beam 100 a due to the ExB deflector103. If this aberration must be corrected, another ExB deflector 106 forcorrecting the aberration is disposed between an illuminating systemcondenser lens 102 and the ExB deflector 103. The illuminating electronbeam 100 a deflected by the ExB deflector 103 so as to go along an axisperpendicular to the wafer 104 is formed by an objective lens 107 as aplanar electron beam entered in a direction perpendicular to the surfaceof the specimen wafer 104. On the focal plane of the objective lens 107is formed a finer cross-over by the illuminating system condenser lens102. Thus the electron beam can be illuminated onto the specimen wafer104 just in parallel. A region of the specimen wafer 104, in which theilluminating electron beam 100 a is illuminated, is an area as large as,for example, 2500 μm², 10000 μm², or the like.

The specimen wafer 104 mounted on a wafer stage 108 receives a negativevoltage almost equal to or slightly higher larger absolute value thanthe accelerating voltage of the electron beam. This negative potentialworks on the illuminating electron beam 100 a so that it slows down justbefore reaching the wafer 104 and pulled back upward to become asreflecting mirror electrons, thereby it does not collide the wafer 104in most cases. The voltage applied to the wafer 104 is supplied andcontrolled by a wafer voltage controller 109. In order to make theilluminating electrons reflected in the vicinity of the wafer 104, adifference from the accelerating voltage of the illuminating electronbeam 100 a is required to be adjusted accurately and the wafer voltagecontroller 109 and the electron gun controller 105 are controlled sothat they are interlocked with each other.

Mirror electrons flying from the wafer side includes information relatedto an electrical defect of an object circuit pattern formed on the wafer104. Thus its image is formed with use of an electron imaging opticalsystem to be fetched in the apparatus as an image for determiningwhether there is a defect in the pattern or not. The mirror electronsare focused by the objective lens 107. And the ExB deflector 103 iscontrolled so as not to deflect an electron beam advancing from below,so that the mirror electrons go up perpendicularly as are, thenmagnified and projected by an intermediate lens 110 and a projectionlens 111 at an image detection part 112. In FIG. 1, only one projectionlens 111 is used, but a plurality of lenses may be composed into aprojection system to provide a higher magnification and correctdistortions of images. The image detection part 112 converts an image toan electrical signal and sends a distribution of the local chargingpotential of the surface of the wafer 104, that is, a defect image to animage processing part 112. The electron optical system is controlled byan electron optical system controller 113.

Next, the image detection part 112 will be described. A fluorescentplate 112 a, an optical image detector 112 b, and an optical imagetransmission system 112 c are used for optical coupling to convert amirror electron image to an optical image and detect the image. In thisembodiment, an optical fiber bundle is used as the optical imagetransmission system 112 c. The optical fiber bundle consists of the samenumber of thin optical fibers as the number of pixels and it cantransmit optical images efficiently. In case where a fluorescent imageis used with a sufficient light, the optical transmittance may be setlower. In such cases, instead of the optical fiber bundle, an opticallens is used and an optical image on the fluorescent plate 112 a isformed by the optical lens on a light detecting surface of the opticalimage detector 112 b. Furthermore, an amplifier is inserted in theoptical image transmission system to transmit an optical image with asufficient light. The optical image detector 112 b converts an opticalimage formed on the light receiving plane to an electrical image signaland outputs the signal. As the optical image detector 112 b, an TDIsensor is used. The TDI sensor uses a time delay integration (TDI) typeCCD.

The image processing part 116 is composed of an image memory 116 a and adefect determination part 116 b. The image memory 116 a inputs electronoptical condition, image data, and stage position data from the electronoptical system controller 113, the image detection part 112, and thestage controller 115 respectively and stores the image data by relatingit to the coordinate system used on the specimen wafer. The defectdetermination part 116 b uses image data related to the coordinates onthe wafer and compares it with a preset value or with an adjacentpattern image or an image of the same pattern position in an adjacentdie, or the like with use of various defect determination methods so asto determine a defect. The defect coordinates and an intensity of itscorresponding pixel signal are transferred to and stored in theinspection apparatus controller 117. The user sets any one of thosedefect determination methods or the inspection apparatus controller 117selects a method corresponding to the object wafer type in advance.

The inspection apparatus controller 117 inputs/outputs conditions foroperating each part of the apparatus. The inspection apparatuscontroller 117 inputs beforehand various preset conditions such aselectron beam accelerating voltage, current conditions for electronoptical devices, wafer stage moving speed, timing for acquisition animage signal from an image detection element. The inspection apparatuscontroller 117 controls the controller of each element as an interfacewith the user. The inspection apparatus controller 117 may be composedof a plurality of computing devices connected to each another through acommunication line and having a specific function. The apparatus furtherincludes user interface device 118 with a monitor.

In the mirror electron imaging type wafer inspection apparatus, theelectron beam hardly collides with the object wafer. Thus the specimenwafer may not be charged sufficiently in some cases. To detect anelectrical defect, however, the wafer must be charged sufficiently tocause a difference from that of normal parts. The present invention hassolved this problem by mounting pre-charging devices 119 a and 119 b.Those devices are controlled by a pre-charging controller 120. Acharging potential formed on the wafer by the pre-charging devices 119 aand 119 b is used not to disturb the status of the electron beam that isreflected in the vicinity of the wafer surface. Thus the pre-chargingcontroller 120 is interlocked and controlled together with the wafervoltage controller 109 and the electron gun controller 105.

FIG. 3 is a first embodiment of a screen on which the user operates theinspection apparatus. This screen 301 is an “inspection conditionsetting screen” on which the user select an inspection speed and aninspection sensitivity or part of the screen. The screen 301 belongs tothe user interface device with a monitor 118. A graph 302 displayed onthe screen 301 has a horizontal axis that indicates a pixel size D and avertical axis that indicates an inspection speed S. In the graph 302,the inspection speed S means an area on a wafer surface to be inspectedper unit time and it is represented by an inspection area (cm²/h) perhour. The user may select this unit to make it easier to understand. Forexample, the unit may be the number of wafers to be processed per houror an inverse number to define a processing time of one wafer and a timerequired for a unit area inspection (e.g., h/cm²).

In the graph 302, a range from 0 cm²/h to 600 cm²/h is shown. The pixelsize D is represented by a value corresponding to an actual size on theobject wafer. It is within a range from 0 nm to 250 nm. The graph 302also has a plurality of characteristic straight lines 303. Thesestraight lines are used for different cycle P values of the TDI sensorrespectively. The graph 302 uses values of 100 to 700 kHz selected as Pvalues. The width L of an inspection image is displayed on an inspectionimage width display part 304. In this example, it is set as 60 μm. Aplurality of conditions are displayed as a pull-down menu for this valuewhen the user clicks the selection arrow 305. The user can select andchange any of the conditions. If the user selects another value, a newlycalculated straight line is displayed as shown in FIG. 4. FIG. 4 showsan example in which 120 μm is selected as an L value. The L value hasits upper limit, which depends on the aberration of the objective lens.If the value goes over 200 μm, the distortion and the resolutiondegradation in marginal area of the field of view advance significantly.Consequently, the upper limit of the field of view usable as aninspection image is about 200 μm×200 μm.

The user can search an inspection speed and a pixel size by moving awhite arrow pointer with a mouse on the graph 302. The values of theinspection speed, pixel size, TDI cycle calculated from the position ofthe pointer on the graph 302 are displayed in a display field 307 at thebottom of the screen. The user can select conditions with reference tosuch concrete values. In the graph 302, not only the values on straightlines, but also values between straight lines are calculated from thepointer position and displayed.

When conditions are determined on the graph 302, the user clicks themouse button (not shown) or press a specific key on the keyboard (notshown) to fix the conditions. Those conditions are sent to thecontroller of the inspection apparatus when the user clicks the [ENTER]button 308 on the screen, then those conditions are converted todetailed operation conditions of the apparatus. Each of those conditionshas its upper limit, which depends on the specifications of theapparatus. For example, if P=700 kHz is the upper limit in thespecifications of the TDI camera and a condition is set in a region over700 kHz, the condition is ignored.

The user can determine values of a set of the pixel size, inspectionimage width, and TDI sensor operation cycle with reference to thedrawing.

Using the condition setting method in this embodiment makes it possiblefor the user to set an inspection speed of the mirror electron imagingtype wafer inspection apparatus without trial and error.

Second Embodiment

In the first embodiment, the user determines conditions for operatingthe inspection apparatus with reference to mainly the values ofinspection speed and pixel size and the relationship between the defectdetection sensitivity and the pixel size is not clear. In this secondembodiment, therefore, the horizontal axis of the graph displayed on theinspection speed S setting screen is used for defect detectionsensitivity, thereby the user comes to know the relationship between thedefect detection sensitivity and the pixel size intuitively. Instead ofthe horizontal axis, the vertical axis may also be used for the defectdetection sensitivity.

FIG. 5 shows a schematic diagram of the inspection speed S settingscreen displayed on the user interface device with a monitor 118 of themirror electron imaging type wafer inspection apparatus. The useroperation screen shown in FIG. 5 is displayed on the monitor of themirror electron imaging type wafer inspection apparatus or mirrorelectron imaging type specimen inspection apparatus. Unlike that shownin FIG. 3, the horizontal axis of the graph 501 is used for the defectdetection sensitivity. Explanations of the same items such as thepointer, the characteristic curve, etc. as those shown in FIG. 3 will beomitted to simplify the description.

The relationship between the pixel size and the defect detectionsensitivity is based on the magnification function of defect imagesspecific to the mirror electron imaging type wafer inspection apparatus.An inspection object image of the mirror electron imaging type waferinspection apparatus is obtained by imaging a distortion of anequipotential surface caused by existence of a defect. FIG. 6 is adiagram for describing principles of such mirror electron imaging. FIG.6A shows a view of an equipotential surface 603 and a view of atrajectory 604 of illuminating electrons reflected from theequipotential surface 603 when such a protruded defect 601 as a particleand such a recessed defect 602 as a scratch are detected on the objectwafer surface. FIGS. 6B and 6C are diagrams for showing a distortion ofthe equipotential surface 606 and a trajectory 607 of illuminatingelectrons when connecting failure defects 605 a and 605 b exist in vias605 used for connecting to the lower layer wiring embedded in an oxidefilm respectively. In FIG. 6B, the electrically open via 605 a isnegatively charged. In FIG. 6C, the open via 605 b is positivelycharged. In any of the unevenness caused by the shape and the electricaldifference of the wafer surface, the distortion of the equipotentialsurface appear more widely than the actual size of the defect. Inaddition, when the equipotential surface is positioned higher, thedistortion spreads widely while the distortion level is low.Consequently, a larger image is obtained when compared with the actualdefect size by adjusting the mirror electron imaging optical system.This means that defects can be detected even when defect images areobtained with pixels larger than the actual defect size.

FIG. 7 is an example of an inspection image obtained with use of amirror electron imaging method. FIG. 7A shows a schematic diagram of acircuit pattern. This pattern consists of 200 nm×200 nm square vias 702embedded in an oxide film 701 and composed like a matrix patternsarranged in 5 rows×5 columns at pitches of 800 nm. Each normal via iscontinued to a wiring 703 in the lower layer. FIG. 7B is an inspectionimage, that is, a mirror electron image obtained with use of a mirrorelectron imaging method. The size of the via patterns in this mirrorelectron image, except for the center one, is as large as 600 nm, whichis about 3 times the actual one. This magnification is made due to adistortion of the equipotential surface caused by a difference ofvoltage between the via voltage and the voltage of its peripheralinsulation film. In the mirror electron image shown in FIG. 7B, thecenter via 704 has a disconnect defect and its voltage differs from thatof other normal ones by about +1.5V. The size of the mirror electronimage of this defect via 704 is about 1200 nm, which is about doublethat of a normal via and magnified up to 6 times that of the actual viapattern.

It can thus be concluded from those data that the size of a mirrorelectron image is magnified to from 3 times to 6 times the actual sizedue to the via voltage. According to this result, in this embodiment, itis expected to be able to detect defects of patterns up to ⅓ of thepixel size and the horizontal axis of the graph 501 for the inspectionspeed is displayed for the detection sensitivity, which is ⅓ of thepixel. The value indicated by the horizontal axis of the graph 501 shownin FIG. 5 is converted from the value indicated by the horizontal axisof the graph 501 shown in FIG. 3 on the basis of the above detectionsensitivity information. The calculation for converting a value of thehorizontal axis or vertical axis such way is executed by a computingdevice built in the inspection apparatus controller 117 or userinterface device with a monitor 118. In the same way, the relationshipbetween the detection sensitivity and the pixel is stored in the memorymeans built in the inspection apparatus controller 117 or in the userinterface device with a monitor 118. As the memory means, for example,any of a memory, a hard disk, etc. may be used.

Next, a description will be made for how to transmit such conditions asuser specified inspection speed, etc. to the electron optical system andthe wafer stage.

FIG. 8 shows a schematic diagram of a hardware configuration of a mirrorelectron imaging type wafer inspection apparatus in this embodiment. InFIG. 8, the same reference numbers will be used for the components ofthe same functions and operations as those shown in FIG. 1. In themirror electron imaging type wafer inspection apparatus shown in FIG. 8,the inspection apparatus controller 117 is provided with a conversionpart 801. Conditions for inspection operations inputted by the userthrough the user interface device 118 are sent to the inspectionapparatus controller 117. In this embodiment, the inspection apparatuscontroller 117 is provided with a condition conversion part 801.Conditions inputted through the user interface device with a monitor 118are values of the pixel size D, inspection speed S, TDI camera imageacquisition cycle P, and size of the field of view L. The moving speedVs of the wafer stage 108 is calculated on the basis of those values.The Vs is determined by the following relational expression according tothe TDI camera image acquisition cycle P and the pixel size D.

Vs=P×D

This Vs value is sent to the stage controller 115. The stage controller115 controls a stage driving mechanism by monitoring the stage positioninformation received from the position detector 114 so as to keep thespeed Vs while the stage is moving. The TDI camera image acquisitioncycle P is sent to the condition conversion part 801 as is. Thecondition conversion part 801 controls the TDI camera image acquisitioncycle so that the image acquisition is synchronized with the stagemovement. The pixel size D, as well as a preset pixel size Dp on the TDIcamera light detecting surface are used to calculate a magnificationDp/D of the imaging electron optical system. The magnification Dp/D ofthe imaging electron optical system is sent to the electron opticalsystem controller 113 and used to control the voltage and theelectromagnet current applied to the objective lens 107, theintermediate lens 110, and the projection lens 111 respectively. Thevoltage and current conditions of each electron optical element of theimaging optical system with respect to the magnification of the imagingoptical system are stored as a numerical table beforehand in theelectron optical system controller 113 or condition conversion part 801.The voltage and current conditions are determined with reference tothose values in the table. If a magnification value that is not storedin the table is referred to, current and voltage values are determinedby interpolating the values for the nearest magnification value.

The condition conversion part 801 or electron optical system controller113 stores a numerical table that records conditions of both thecondenser lens 102 and the objective lens 107 with respect to the sizeof the field of view L. And upon a user's determination for the size ofthe field of view L, the voltage and current values of the illuminatingelectron optical system are referred to from the numerical table forcontrolling. With such a configuration, the user selected inspectionconditions are reflected correctly in the inspection apparatus.

As described above, therefore, in this embodiment, the user can set suchinspection conditions as inspection speed and defect detectionsensitivity as parameters. Consequently, the user can operate theapparatus more easily.

Third Embodiment

In the second embodiment, a description is made for a user operationscreen on which the defect magnification is set as 3 times. This thirdembodiment enables the user to change the defect magnification.

FIG. 9 shows a user operation screen in this third embodiment. The useroperation screen shown in FIG. 9 is displayed on the monitor of themirror electron imaging type wafer inspection apparatus or mirrorelectron imaging type specimen inspection apparatus. In this thirdembodiment, the description for the same components as those shown inFIG. 5 will be omitted. In FIG. 9, there is only a difference from thatshown in FIG. 5; a defect magnification selection field 901 is provided.The user can select a magnification from a plurality of defectmagnification values by clicking the arrow in the defect magnificationselection field 901. The value of the horizontal axis of the graph 902is corrected by the selected defect magnification, thereby the displayedcharacteristic curve is also corrected.

The user can change the defect magnification according to the objectivelens focal condition, the height of the equipotential surface forreflecting mirror electrons, etc. in the mirror electron imaging. Amirror electron image is always formed due to a distortion of theequipotential surface even when the defect type is an uneven surface ora voltage variation caused by an electrical defect. Consequently, theuser can estimate a defect image magnification in advance by using theheight of the equipotential surface for causing mirror reflection ofelectrons and focal conditions of the objective lens as parameters.

For such an estimate, the user is just requested to obtain a mirrorelectron image with respect to a different focal point of the objectivelens and a different voltage potential value of the wafer and measure amagnification according to the actual defect size by using an Si waferof which size is already known and having a protruded or recessed shapedefect that is already processed. If the defect type is not such a shapedefect, but it is a potential variation, a voltage that causes theequipotential surface to be distorted as much as a distortion generatedby a protruded or recessed shape may be calculated by computersimulation and adjusted precisely with the relationship between theelectron optical condition and the magnification in the shape defect.Because such calculation of a level of a distortion of an equipotentialsurface with respect to a voltage is simple calculation of an electricalfield, it is so easy. Instead of using a standard specimen as describedabove, it is also possible to analyze a trajectory of electrons bycomputer simulation and change the condition of the objective lens,thereby calculating an image to be obtained, then obtaining arelationship with a magnification.

In this embodiment, the inspection apparatus is provided with aninspection condition evaluation device 1001 for holding a table thatstores a condition of the objective lens, a negative voltage value to beapplied to each wafer to change its equipotential surface used formirror reflection, and a defect magnification obtained as describedabove. FIG. 10 shows a schematic diagram of a system provided newly withthe inspection condition evaluation device 1001.

When an inspection is made with a defect magnification using thisinspection apparatus, the equipotential surface for reflecting mirrorelectrons must be kept constant. Thus it is important to keep the wafersurface potential constant. This is why pre-charging devices 119 a and119 b are used. Those charging devices are controlled by a pre-chargingcontroller 120. For example, assume now that a wafer is passed under thepre-charging device, then just under the objective lens and moved justunder the pre-charging device 119 b. In such a case, the wafer surfacepotential is set to a prescribed potential by the pre-charging device119 a. This potential makes it possible to obtain a desired defectmagnification. The potential is given from the numerical table of theinspection condition evaluation device 1001 and controlled by thepre-charging controller 120. As the pre-charging device, for example,such an electron beam illuminating device as a flood gun may be used.After the wafer passes just under the objective lens, the disturbance ofthe equipotential surface potential, caused by slight charging of thewafer when in observation of mirror electrons, must be eliminated so toas return the potential to a required level with use of the pre-chargingdevice 119 b again.

According to this third embodiment, therefore, it is possible tooptimize the such conditions as the inspection time including the userspecified defect magnification, thereby the object semiconductormanufacturing line can be managed efficiently.

Although a description has been made for the preferred embodiments ofthe present invention, the present invention also includes a combinationof the first to the third embodiment described above.

1. An inspection apparatus to inspect a wafer by using an image,comparing: an electron optical system to output an image of aninspection region on a wafer as image signals by radiating an electionbeam on a certain area of the wafer means for forming the image of theinspection region from the image signals a wafer stage to move the waferat a certain speed; and a display to display a result of the inspectionof the wafer, wherein the display displays a relationship among value ofS, D, L, and P on an graph with respect to a plurality of value of LandP respectively by assuming D and S as coordinates axes when L is definedas a length in a direction perpendicular to a moving direction of thewafer of which the image is being obtained in a range of an inspectionimage in the region on which the electron beam is radiated, S is definedas an area of the wafer to be inspected per unit time, D is defined as asize on the wafer, corresponding to a unit pixel of the image, and P isdefined as the image signal acquisition frequency, wherein the displaydisplays a pointer a user can move and displays D and S of a positionthe user selects with the pointer; and wherein the inspection withconditions of the selected D and S is conducted.
 2. The apparatus,according to claim 1, wherein the electron beam is a planar electronbeam (line 1 in page 18 of our spec.)
 3. The apparatus, according toclaim 1, wherein the electron optical system is a projection opticalsystem to output the image signals obtained by projecting the inspectionregion.
 4. The apparatus, according to claim 1, wherein the displaydisplays a plurality of lines in the graph corresponding to each valueof P with respect to an certain value of L.
 5. The apparatus, accordingto claim 4, wherein the graph is changed corresponding to the value of Lthe user selects in accordance with the formula of S=D×L×P
 6. Theapparatus, according to claim 1, wherein the L value is selected within200 microns or under.
 7. The apparatus, according to claim 1, whereinthe D value is displayed as 250 mm or under.
 8. The apparatus, accordingto claim 1, wherein the apparatus further includes means for holding anumerical table in which a condition for operating an electron lenscorresponding to each of D and L values is set beforehand and means fordetermining a condition for operating the electron lens to realize userdetermined values of D and L with reference to the numerical table. 9.An inspection apparatus to inspect a wafer by using an image,comprising: an electron optical system to output an image of aninspection region on a wafer as image signals by radiating an electronbeam on a certain area of the wafer means for forming the image of theinspection region from the image signals a wafer stage to move the waferat a certain speed; and a display to display a result of the inspectionof the wafer, wherein the display displays an graph related to S=D×L×Pwith respect to a polarity of value of L and P respectively by assumingD and S as coordinate axes when L is defined as a length in a directionimage in the region on which the electron beam is radiated, S is definedas an area of the wafer to be inspected per unit time, D is defined as asize on the wafer, corresponding to a unit pixel of the obtained digitalimage, and P is defined as an image signal acquisition frequency in thetime delay integration formula, wherein the coordinate axis is S or S′defined as the number of wafers to be processed per hour, an inversenumber to define a processing time of one wafer or a time required for aunit area inspection by calculating S, and wherein the display displaysa pointer a user can move and displays D and S or S′ of a position theuser selects with the pointer, and wherein the inspection with selectedD and S or S′ is conducted.
 10. The apparatus, according to claim 8,wherein the electron beam is a planar electron beam.
 11. The apparatus,according to claim 9, wherein the electron optical system is aprojection optical system to output the image signals obtained byprojecting the inspection region.
 12. The apparatus, according to claim9, wherein the display displays a plurality of lines in the graphcorresponding to each value of P with respect to an certain value of L.13. The apparatus, according to claim 12, wherein the graph is changedcorresponding to the value of L the user selects in accordance with theformula of S=D×L×P
 14. The apparatus, according to claim 9, wherein theL value is selected within 200 microns or under.
 15. The apparatus,according to claim 9, wherein the D value is displayed as 250 mm orunder.
 16. The apparatus, according to claim 9, wherein the apparatusfurther includes means for holding a numerical table in which acondition for operating an electron lens corresponding to each of D andL values is set beforehand and means for determining a condition foroperating the electron lens to realize user determined values of D and Lwith reference to the numerical table.